The present invention relates to a developing device for a laser printer, facsimile transceiver, copier or similar electrophotographic image forming apparatus. More particularly, the present invention is concerned with a toner layer regulating member incorporated in the developing device for causing a toner to form a thin layer, i.e., substantially a single layer on a toner carrier so as to charge it uniformly and stably.
One of conventional developing devices for the above application includes a toner carrier in the form of a roller or a sleeve, a toner supply roller, an agitator, and a toner layer regulating member. The toner carrier deposits a charged developer or toner on a photoconductive element or similar image carrier on which a latent image is electrostatically formed. The toner supply roller supplies the toner to the surface of the toner carrier. The agitator conveys the toner to the toner supply roller while agitating it. The toner layer regulating member causes the toner to form a layer on the toner carrier while charging it This kind of developing, device is disclosed in, for example, U.S. Pat. No. 5,142,330 (Hirano et al.).
It has been customary to make the toner carrier of aluminum, stainless steel or similar rigid material and to make the toner layer regulating member of silicone rubber, urethane rubber or similar elastic material. The problem with such a combination is that even though the regulating member regulates the toner on the toner carrier, the toner deposits thickly in more than one layer(s) or thinly in less than one layer. Such a toner layer cannot be charged uniformly or stably, failing to produce an attractive image. Specifically, it often occurs that much of the toner is charged to a polarity opposite to the expected one and deposited on the background of a latent image formed on the image carrier to thereby contaminate it.